Fix invite domain URL and improve shared mobile header

app/modules/firm_admin_dashboard/service.py

@@ -286,8 +286,31 @@ ONBOARDING_ROLE_CONFIG: dict[str, dict[str, str]] = {
 }
 
 
-def _public_invite_url(invite_token: str) -> str:
-    base = (get_settings().ERP_PUBLIC_BASE_URL or "").strip().rstrip("/") or "http://localhost:8000"
+def _public_invite_url(request, invite_token: str) -> str:
+    """Build an invite URL for the domain currently used by the Firm Admin.
+
+    Tenant custom domains must remain tenant-specific.  Prefer the request host
+    (including trusted proxy headers) and retain ERP_PUBLIC_BASE_URL only as a
+    defensive fallback for non-HTTP callers.
+    """
+    forwarded_proto = (request.headers.get("x-forwarded-proto") or "").split(",", 1)[0].strip().lower()
+    forwarded_host = (request.headers.get("x-forwarded-host") or "").split(",", 1)[0].strip()
+    request_host = (request.headers.get("host") or "").strip()
+
+    scheme = forwarded_proto if forwarded_proto in {"http", "https"} else str(request.url.scheme or "https").lower()
+    host = forwarded_host or request_host or str(request.url.netloc or "").strip()
+
+    # Reject header-control characters before using a host in a generated URL.
+    if host and not any(ch in host for ch in "\r\n/\\"):
+        base = f"{scheme}://{host}".rstrip("/")
+    else:
+        base = str(request.base_url).strip().rstrip("/")
+
+    if not base:
+        base = (get_settings().ERP_PUBLIC_BASE_URL or "").strip().rstrip("/")
+    if not base:
+        raise ValueError("Unable to determine the public ERP URL for the invite link.")
+
     return f"{base}/invite/accept?token={invite_token}"
 
 
@@ -498,7 +521,7 @@ def create_firm_internal_user(
 
     db.refresh(user)
     invite_token = issue_invite_token(db, user)
-    invite_url = _public_invite_url(invite_token)
+    invite_url = _public_invite_url(request, invite_token)
     email_status = "not_attempted"
     email_error = None
     try: